1. Field of Invention
The invention relates generally to a replacement device for a knee joint, and more particularly, to a device for resurfacing the trochlear groove of a femur that is customized to an individual and to methods for installing and making the same.
2. Description of the Related Art
The human knee joint primarily includes three parts, anatomically referred to as the femur (thighbone), the tibia (shinbone) and the patella (kneecap). The knee joint is then further subdivided into two joints: the patella-femoral joint (space between the kneecap and distal anterior surface of the thighbone) and the tibia-femoral (space between the thighbone and shinbone).
During normal bending and straightening of the leg, the patella (kneecap) slides over the femur (thighbone) within a groove that is located on the front distal surface of the femur. This groove is referred to as the trochlear groove. Several types of abnormalities can occur with the movement of the patella over the femur. For example, the patella may dislocate or slip out of place, it may fracture, or develop a tracking problem. Normally, the patella tracks, or glides within the central region of the trochlear groove. A tracking problem occurs when the patella no longer remains centered within the groove as it glides over the femur. The resulting abnormal biomechanics can cause chronic pain in the joint and if left untreated, it can lead to degenerative arthritis.
The distal end of the femur (within which resides the trochlear groove) is covered with articular cartilage. This cartilage functions as a cushion between the femur and the tibia. In arthritis of the knee joint, the articular cartilage breaks down, either from abnormal wear as mentioned above, or from injury, age, congenital predisposition, inflammatory arthritis, or obesity, etc. When this cartilage breaks down, the cushion is lost, resulting in pain, swelling, bone spur formation and/or decreased range of motion of the knee joint.
Due to the inability of damaged cartilage to repair itself after injury, the range of treatment for patients with unicompartmental disease involving the patella is limited. The most commonly prescribed treatments included soft tissue releases and/or realignment of the patellar tendon, patellectomy, where the patella is completely removed, or a total knee replacement with a standardized patello-femoral-tibial prosthesis. In certain instances none of these procedures may be desirable or effective. For example, the soft tissue procedures may not work. A patient having undergone a patellectomy is left partially crippled due to the loss of the kneecap, which served to hold the joint together. Additionally, these patients often still suffer from pain due to contact of the remaining tendon moving directly over the groove. A total knee replacement with a standardized prosthesis is also far from ideal because much of the femur bone must be carved away in order to xe2x80x9cfitxe2x80x9d the distal surface of the femur to the standardized prosthesis. Additionally, the patients are often young and are likely to require replacement of the prosthesis. Each revision operation is more difficult. Therefore, there still is a need for a better treatment of patient""s with degenerative arthritis of their patella-femoral joint.
The present invention provides a replacement device that is customized to each individual knee joint. Due to the xe2x80x9cfittingxe2x80x9d of the replacement device to the patient""s femur, instead of the reverse as is the case with standard prosthetic devices, the patient""s original range and force of motion (kinematics) through the knee joint is preserved and the patient does not suffer from device-related pain. Also included is a method for making a customized replacement device and a marking template for such a device. Bone stock removal is limited and functionally is maximized.
The present invention is directed toward a custom replacement device for resurfacing an articulating or joint surface of the femur and methods of making and installing such a device. This custom replacement device overcomes the problems associated with prior knee joint replacement devices or prostheses in that it is made specifically to fit the trochlear groove surface (surface over which the patella slides) of a femur from an individual patient. Thereby creating a xe2x80x9ccustomizedxe2x80x9d replacement device for that individual femur.
The replacement device is substantially defined by four outer points and first and second surface areas. The first of four points is defined approximately as being 3 to 5 mm from the point of attachment of the anterior cruciate ligament to the femur. The second point is defined approximately at or near the superior edge of the end of the natural cartilage. The third point is defined approximately at the top ridge of the right condyle. The fourth point is defined approximately at the top ridge of the left condyle. The first surface area is customized to substantially match the bone surface area of the trochlear groove of the femur. The second surface area has a tracking path that is approximately perpendicular to the end of the condyles of the femur. The thickness between the first and second surface areas may be approximately between 2 mm and 6 mm. To couple the replacement device to the femur, a pin protruding from the first surface area may be used to penetrate an opening in the femur prepared by a surgeon. Boney ingrowth may secure the prosthesis or bone cement may be used.
The replacement device can also include a customized drill guide that is substantially defined by first and second surface areas. The first surface area is customized to the surface area of the trochlear groove of the femur. The second surface area includes a hole that is aligned substantially to the pin to assist in drilling the opening into the femur for the pin.
In accordance with one aspect of the present invention, these and other objectives are accomplished by providing a replacement device having a top surface; a bottom surface; the bottom surface substantially formed to match the trochlear groove surface of a femur; and the top surface substantially tracking the trochlear groove of the femur.
In accordance with another aspect of the present invention, these objectives are accomplished by providing a system for installing a replacement device to a distal end of a femur having a trochlear groove surface, comprising: a marking template, wherein: the marking template has a back side substantially matching the distal end of a femur; and an opening through the marking template; a drilling apparatus to form a hole on the distal end of the femur assisted by the opening in the marking template; and a replacement device, wherein: the replacement device has a bottom side substantially matching the distal end of the femur; and a pin protruding from the bottom side of the replacement device adapted to insert into the hole on the distal end of the femur.
In accordance with yet another aspect of the present invention, these objectives are accomplished by providing a method of making a replacement device, comprising the steps of: forming a model of a distal end of a patient""s femur; forming a first mold from the model, wherein the first mold has a bottom side that substantially matches the trochlear groove of the patient""s femur, wherein the first mold has a top side opposite of the bottom side; coupling a peg on a predetermined location on the bottom side of the first mold; shaping the top side of the mold to substantially track the trochlear groove of the patient""s femur; forming a second mold from the first mold; and pouring viscous material into the second mold to make a replacement device.
In accordance with still another aspect of the present invention, these objectives are accomplished by providing a replacement device having a bottom side that substantially matches the trochlear groove of a patient""s femur, wherein the bottom side of the replacement device has a pin at a predetermined location; providing a marking template having a back side that substantially matches the trochlear groove of the patient""s femur, wherein the marking template has an opening corresponding to the predetermined location of the pin; removing the cartilage from the distal end of the femur; positioning the marking template about the femur substantially similar to the desired installed position of the replacement device; drilling a hole on the distal end of the femur though the opening of the marking template; removing the marking template from the femur; and inserting the pin of the replacement device into the hole of the femur to install the replacement device on the desired location of the femur.
Alternatively, a method of forming a customized replacement device for a femur will include the steps of duplicating the surface of the distal anterior femur from an individual; and using the duplicate to form a back surface of the customized replacement device and/or a customized marking template.